1. Field of the Invention
The invention relates to a gyroscopic instruments and more particularly to a gyroscopic rate sensor of the flexible disc rotor type.
2. Description of the Prior Art
Gyroscopic systems which use a spinning flexible disk for measuring a rate of attitude change are well known in the art. See for example, U.S. Pat. Nos. 3,323,377 and 4,498,340. As disclosed therein, a this flexible disc is mounted on the end of a shaft and spun at a high rotational velocity by a spin motor. Rotation of the gyro housing about an axis orthogonal to the spin axis results in a precessional deflection of the flexible disc rotor relative to its plane of rotation and proportional to the rate of such rotation. Electrical transducers are provided for generating electrical signals proportional to the disc rotor deflection and hence to the precession and are therefore proportional to the input angular rates.
The prior art systems have not yet resulted in a successful product capable of practical application. With a spring element as the dominant coupling between the sensing rotor and the drive shaft, the spin axis of the rotor describes a cone of diminishing amplitude about it steady state position with respect to the shaft spin axis in response to a step rate input. This results in an apparent underdamped oscillatory output on the sensing axis and a decaying oscillation in the quadrature axis, and hence exhibits a poor dynamic response.
Further, in order to provide an accurate measurement of precession rate about two perpendicular axes, each perpendicular to the spin axis, it has been necessary to provide two pairs of transducers or pick-offs, one pair for each sensing axis, with each pair being electrically connected in push-pull fashion, and the outputs differentially added to produce an output signal proportional to the direction and magnitude of the input angular rate. Since the pickoffs measure displacement of the rotor with respect to the case and precession rates cause displacement of the rotor spin axis with respect to the shaft spin axis, null instability results from any minutes shifting of the pickoff elements with respect to the shaft spin axis.
These errors are substantially reduced in the present invention by modifying the flexible disc rotor to minimize its spring restraint, adding a closely spaced rigid plate adjacent to the rotor disc on the spinning shaft, and filling the rate sensor with a gaseous atmosphere in order to provide viscous gaseous restraint. As this restraint acts in quadrature to the spring restraint, it does not adversely affect the dynamic response.
Further, null stability is enhanced by arranging the pick-off to sense spin frequency oscillation of the rotor substantially with respect to the shaft rather than rotor displacement with respect to the housing.